In electronic data processing layouts, printers are used for the output of texts, data, and graphic information. The transfer of printed symbols onto a carrier, e.g., paper, is accomplished by a printing head. Never printers are characterized by the fact that they can contain printing heads of various types in a single printer housing. Such a printer is described, e.g., in German Patent (OLS) No. 3,511,386. In this device, the printing heads in a printing station can be interchanged, while a printer can contain several such printing stations. This printer has a simple basic housing, which can be very economically produced in great unit quantity. Depending upon its anticipated use, the basic housing unit can be equipped with various printing heads, while the decision on specific equipment options can be delayed until final assembly. In this way, it is possible to achieve a great variety of types of printers and a high level of fabrication economy. Devices of this type are used, e.g., as passbook printers, cash voucher printers, etc.
There is a whole series of printing processes, which have led to differing functional principles and designs of printing heads. For transferring the printed symbols onto the carrier, the printing heads have a multitude of printing elements, which are variably designed in keeping with the different printing processes. Among these, the mosaic printing process has attained special significance. In this process, the symbol pattern is made up of colored dots assembled together in the manner of a mosaic by the printing elements. In each instance, these printing elements are actuated by a servo component, the electrical resistance of which can be, in addition to an active resistance, also a reactance or an impedance with a capacitive or an inductive component. In an ink-mosaic printing process, such a printing element consists of a jet, which, when a piezoelectrical servo component is actuated by an electrical impulse, sprays a droplet of ink onto the data carrier to form a colored dot. The printed symbol is formed by the combining of many such individual colored dots in a grid. In another process, which may be referred to as pin printing, the individual printing elements are designed as pins. By means of an electromechanical servo component responding to the dynamic effect of a current passing through a coil, pins are directed outward to press an inked ribbon against the print carrier, whereby a dotted symbol pattern is also formed. Finally, there is also the thermal printing process, in which the printing element contains an ohmic resistor as its servo component, which heats up when a current is introduced. By means of a liquescent color ribbon, dotted print symbols are transferred to the print carrier or formed directly on a heat-sensitive recording carrier.
For carrying out the printing operation, the printing head must be provided with control signals, which have a definitive value range and represent control parameters. These control parameters are produced in a control unit, to which the information to be printed is provided. Important control parameters are, e.g., the selection of the printing element for printing a mosaic dot or a combination of printing elements for printing a symbol, as well as the amount of energy, which must be provided to the respective printing elements for executing the printing action. Another important control parameter determines the timing and the duration of the printing action. By virtue of the time-sequencing control of the printing action, the location of the printed symbol on the carrier is determined independently of the relative displacement between the printing head and the carrier. Various types of printing heads differ in their control parameters. When different types of printing heads are to be installed in one printer, the control parameters to be readied by the control unit must also be matched to the type of the printing head. Inasmuch as the control parameters for the various types of printing heads are known, it is possible to construct a control unit in such a way that it contains all of the control parameters for the various types of printing heads planned for a printer and to call them up as needed. The control parameters can, e.g., be stored as data in a memory or preestablished as switchable circuits. In order that the control unit can ready the control parameters to be furnished to a printing head, it requires information relative to the type of the printing head to be addressed.
This can be accomplished in such a way that a trained operator determines in a manual check the type or kind of the printing head and provides this information to the control unit by actuating a coding switch of the control unit. This procedure includes the inherent danger of erroneous operation as a result of improper identification of the printing head or incorrect switch setting. Furthermore, mechanical structures necessary to preclude inadvertent or unauthorized access to the coding switch. Consequently, it would be desirable for the transmission of information relative to the type of the printing head to be automatically elucidated by the printer in the interest of preventing, with a very high degree of probability, erroneous operation of the printer.